Importance

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Abstract

A disaster prevention monitor is disclosed in which the power consumption during a line monitoring process is reduced, and a disconnection or a short circuit of control lines can be detected by using a single switching means. A central station has a monitor command transmitter for transmitting a monitor command signal to initiate monitoring of power and control lines. A terminal or repeater station has circuitry for controlling the connection of control lines between a line monitor and power lines. During normal conditions, the control lines are not connected to the power lines, but become so connected only in response to a command from the central station. A line monitoring command causes generation of a negative voltage which is applied to line monitoring circuitry to actuate such circuitry for monitoring the status of the power and control lines.

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First Claim